This invention relates to an arrangement for supplying oil to journal bearings for use in fan drive systems for turbofan engines.
Turbine engines use epicyclic gear systems to drive fans or propellers during engine operation. Journal bearings are utilized in the gear systems to transfer torque between planet gears and corresponding support shafts. Oil is supplied from an oil system to lubricate each of the journal bearings. An oil pump maintains pressure within the oil system to ensure each of the journal bearings receives an adequate supply of oil.
During operation, the gas turbine can be shut down for various reasons. When the gas turbine is not operating, the oil pump may also shut down. However, due to the force of the wind, the fan will continue to rotate, or windmill, even while the engine is not driving the fan. Without some oil supply, the journal bearings may seize and stop engine rotation.
The required oil supply for a windmilling fan is significantly reduced compared to driven fan operation. Thus, the size of the oil lines used for driven fan operation is larger than the size of the oil lines needed for a windmilling fan. A pressure drop across all bearings would occur if using the same oil lines at significantly reduced flow, resulting in only some of the bearings receiving oil. Also, in the event of system oil loss, a separate system to supply oil to the bearings for windmilling is required.
Accordingly, providing an improved arrangement to lubricate journal bearings during windmilling fan operation is desired.